1. Technical Field
The present application relates to an apparatus for detecting temperature of switching elements, and more particularly, to the apparatus provided with an overheat detection circuit which is for detecting overheat at semiconductor switching elements.
2. Description of the Related Art
Conventionally, temperature detecting apparatuses has been employed in various systems. For example, Japanese Patent Application Laid-open Publication No. 2010-199490 discloses a temperature measurement apparatus as a temperature detecting apparatus having a temperature sensing element that detects temperature of a target object. This apparatus additionally includes an overheating detection circuit that detects overheating of the target object based on the detection result of the temperature sensing element.
The temperature measurement apparatus detects the temperature of an IGBT (insulated gate bipolar transistor) device and protects the IGBT device from overheating. The temperature measurement apparatus includes a temperature sensing diode and an IGBT protection circuit. The temperature sensing diode detects the temperature of the IGBT device. The temperature sensing diode allows a constant current to flow and outputs voltage based on the temperature of the IGBT device. The IGBT protection circuit detects overheating of the IGBT device based on the temperature detected by the temperature sensing diode and protects the IGBT device. The IGBT protection circuit supplies a constant current to the temperature sensing diode and compares the voltage of the temperature sensing diode with a predetermined threshold thereby detecting overheating of the IGBT device. The IGBT protection circuit outputs an IGBT protection signal when detecting overheating of the IGBT device.
Moreover, the above-described IGBT protection circuit may include a breakage detection circuit. The breakage detection circuit detects a wire-breakage of a temperature sensing diode or the like based on the voltage at a connection terminal that connects the temperature sensing diode.
There is a requirement that the IGBT protection circuit is used without requiring the temperature sensing diode. However, when the temperature sensing diode is not used, the temperature sensing diode is not connected to the connection terminal so that the breakage detection circuit erroneously detects a breakage of wire. Therefore, a dummy resistor in which constant current flows to output a constant voltage regardless of a temperature variation is connected to the connection terminal. As a result, the breakage detection circuit can be configured to avoid erroneously detecting wire breakage. In this regard, a dummy resistor is necessarily used. Therefore, considering the breakage detection circuit is used for a power conversion apparatus in which a plurality of IGBT devices are disposed, the number of components increases. Accordingly, the power conversion apparatus cannot be shrunk in its size and manufacturing cost increases as well.